Running start "" "MinecraftLauncher.exe" --workDir "data\.minecraft" now creates the nativelog.txt within C:/Users/<user>/AppData/Roaming/.minecraft, though still uses /data/.minecraft as the working directory for versions and saves etc. As seen at https://pastebin.com/HW7uUJTR, all of the directories are set correctly except for the Application Data directory. Including set "APPDATA=data" did not fix the issue.